Climate change may not have been on the official Rio+20 agenda, but that didn’t stop mayors from megacities around the world from making major headway on the issue. At the Rio+20 conference on Tuesday, the network of C40 city leaders announced new data showcasing the fact that these cities' initiatives could cut 1.3 billion metric tons of carbon emissions by 2030.

At the decidedly urban event—perched in a colorful, high-tech auditorium miles from Rio+20’s official negotiations in the suburbs—Mayors Bloomberg (NYC), Paes (Rio de Janeiro), Park (Seoul), and Tau (Johannesburg)—as well as President Clinton (via video) and other leaders—made a compelling case for global action through cities. The mayors asserted that cities are proving to be the most effective government entities in addressing global climate change. In addition to announcing goals to reduce 1.3 billion metric tons of carbon emissions by 2030, leaders cited already-taken actions that will cut 248 million tons of greenhouse gases by 2020. The cities’ achievements contrast with international negotiations (and some national governments), which have been unable to agree to binding CO2 reduction targets.

Cities Are Already Taking Action

Cities certainly are playing a vital role in tackling a global problem. Mayors are more directly accountable to their constituents than national leaders on quality-of-life issues. Cities also directly control the majority of the big, greenhouse gas-emitting urban systems— such as transportation, waste, electricity, and building regulations. And whereas cities have been rightfully criticized as the source of many global climate challenges– they account for 75 percent of global CO2 emissions, for example– they’re also proving to be engines of innovative solutions to address those problems.

Consider some initiatives already under way:

Rio’s new TransOeste BRT (Bus Rapid Transit) corridor – on which WRI’s EMBARQ program provided key technical assistance – is the first of four lines that will carry 1.2 million people in Rio every day in safe, fast, low-carbon transit.

San Francisco aims to be a zero waste city by 2020, and already recycles or composts 77 percent of its waste, avoiding tons of planet-warming methane gas emissions.

Of course, national governments also have a very important role in curbing climate change. They can provide finance to help cities make real change, as well as establish environmental standards to ensure cohesive approaches across political boundaries. But in the absence of faster and more ambitious progress on the international— and in many cases, the national— climate agendas, cities have the opportunity to take the lead in confronting what is undoubtedly a global challenge.

Cities can do more, too. Carbon-emission reduction targets remain self-referential (e.g. “reduce by 20 percent” or “reduce by 1.3 billion tons”), rather than tied to specific levels that would be necessarily sustainable. And many city mayors still need more political will to take big steps.

Also, climate remains just one narrow aspect of sustainability. Quality of life issues are core to a sustainable city.

On this point, the mayors’ panel was confronted with the challenging question of whether huge cities really can deliver good quality of life at such huge scale (10-20 million people). Mayor Bloomberg said that immigrants, the main source of population growth for most cities, are sources of intellectual capital, talent, entrepreneurial courage, and diversity that lead to innovation, culture, and ultimately, better quality of life. His strategy is not to subsidize business to create jobs, but to improve quality of life, which in turn will attract business and entrepreneurs. Mayor Tau underscored that Johannesburg will double in population by 2030, and that social inclusion and provision of basic services must be priorities. Mayor Paes of Rio emphasized the urgency of taking action now - which cities can do.

So what do you think? Could an effective global climate strategy focus on cities? Could cities address both climate and quality of life successfully? Leave your thoughts in the comments section below.